We have obtained partially purified preparations of lipoprotein lipase from rat adipose tissue and of a factor in serum which releases lipoprotein lipase from isolated adipocytes. Purification will be continued until preparations which show single protein bands on gel electrophoresis are obtained. We will attempt to prepare antisera to these purified proteins and also to post heparin plasma lipoprotein lipase purified by available methods. With regard to our continuing exploration of metabolic regulation of two lipoprotein lipase fractions in rat adipose tissue, a study of the role of insulin in this regulation will be carried out. We plan to locate these lipoprotein lipase fractions within adipose tissue. These studies will be extended to aortic tissue also.